A device to measure flow and quantity of heat is known from DE-OS 32 44 668. To measure quantity of heat, the difference of initial and final temperature of a heat circuit, the flow cross-section in form of the valve stroke as well as the pressure difference produced at the shut-off device are ascertained, are transmitted to an electronic logic unit, are combined, displayed, summed, and again displayed.
DE-OS 32 10 901 discloses a device to ascertain the quantity of hot water and the heat consumption whereby the valve opening width is measured and the hot water quantity is derived therefrom. The effective differential pressure is not measured, so that relatively great measurement errors necessarily occur when the differential pressure varies.
DE-OS 37 00 898 discloses a quantity regulating valve in which the pressure and the temperature before and after the valve as well as the opening cross-section of the valve are measured and are processed by a computer.
EP-OS 0 309 643 furthermore discloses a quantity regulating valve in which the means for the measuring of the differential pressure are located above the valve, inside the enclosing body.
Even when the actual pressure difference is measured, the problem remains that measuring errors which cannot be tolerated occur with very low flows. In the DE-Z "Fernwarme international" 17(1988), volume 1, pages 23-35 the occurring problems are pointed out. In flow measuring and control systems based on the principle of effective pressure measurement, the problem basically remains that the measured pressure difference represents a square function of the flow speed. If the measure of the differential pressure is sufficiently precise in a range from 10 to 100% of the nominal flow of the measuring device, i.e. with a ratio 1:10, the corresponding flow-through speeds are at a ratio of 1:.sqroot.10. It follows from this that ordinary measuring devices for flow speeds have only a small measuring range of sufficient measuring precision. Therefore the measuring range is also correspondingly small in heat measurements.
It is known that especially in transition periods, extremely low flows often occur, which are beyond the measuring range of the measuring means.
The instant invention has therefore as its ob]ect to create a device to measure flow and heat quantities at low manufacturing cost, having a measuring range of sufficient precision that is distinctly greater than that of known devices.